In the frame of the ESREL special session on ARAMIS project, this paper aims at presenting the work carried out in the first Work
Package, devoted to the definition of accident scenarios. This topic is a key-point in risk assessment, and serves as basis for the whole risk
quantification. A first part of the work aims at building a Methodology for the Identification of Major Accident Hazards (MIMAH), which is
carried out with the development of generic fault and event trees based on a typology of equipment and substances. This work is coupled with
an historical analysis of accidents. In a second part, influence of safety devices and policies will be considered, in order to build a
Methodology for the Identification of Reference Accident Scenarios (MIRAS). This last one will take into account safety systems and lead to
obtain more realistic scenarios.